Gear pump or motor



March 21, 1967 YASUO KITA 3,309,997

. GEAR PUMP OR MOTOR Filed June 2, 1965 4 Sheets-Sheet l 38 48 49a 48aSkis FIG. v1. 42

INVENTOR YAsuo KIT'A BY 7 7 ,iu ou, [Quvflm ATTORNEY March 21, 1967 s oK|TA I 3,309,997 Q GEAR PUMP OR MOTOR Filed June 2, 1965 4 Sheets-Sheet2 INVENTOR YAsuo Kn-A BY maym wmyavy ,AQ/Ifi 36a AT NEY March 21, 1967suo KlTA 3,309,997

GEAR PUMP OR MOTOR Filed June 2, 1965 4 Sheets-Sheet 5 FIG. 5. 25 f FF/G.6c1. b FIG 5b 5' i 25 30 46 l 23 44 90 33 94 FIG. 7. 28 24 45INVENTQR Yhsue K WA ATTORNEY March 21, 1967 YASUO KITA 3,309,997

GEAR PUMP OR MOTOR Filed June 2, 1965 4 Sheets-Sheet FIG. 8;

United States Patent 3,309,997 GEAR PUMP OR MOTOR Yasuo Kite, Kyoto,Japan, assignor to Shimadzu Seisakusho Ltd, Kyoto, Japan Filed June 2,1965, Ser. No. 460,760 Claims priority, application Japan, July 31, 1964(utility model), 39/61,017 (utiiity model), 39/61,0ll8 (utility model),39/61,!)19, 39/43,759

7 Ciaims. (Cl. 103-126) This invention relates to gear pumps or motors,and more particularly to an improved construction for sealing gearperipheries.

Gear pumps or motors are conventionally made with an intermediatesection including intersecting arcuate chambers to accommodate thegears, and end closures secured to the ends of the intermediate sectionto form the chamber ends. The intermediate section is formed either as aseparate member from each of the end closures or as an integral partwith one end closure. In any case, the gear chamber is subjected to apressure gradient which varies from inlet pressure in the area adjacentthe pump inlet to discharge pressure in the area adjacent the dischargeside of the pump. Therefore, the portion of the gear peripheries nearthe pump inlet is subjected to less pressure tendency than the portionsof the gear periphcries near the pump outlet. This unbalanced conditiontends to urge the gears to the gear chamber wall at the inlet side ofthe pump and results in torque loss due to friction of tooth top of thegears. The torque loss increases the power required to turn the pump. Incase of gear motors, it decreases the output.

In conventional gear pumps or motors, problems are also encountered dueto dimensional interference between cooperating members and partsconstituting the pump or motor assemblies. Highly accurate location andfine machining of the members are required to avoid dimensionalinterference therebetween. For example, the gear shafts must be exactlylocated in the respective required positions within the gear casingconsidering the pitch circles of the gears. The gear casing wall forc0vering the gear peripheries in sealing relationship must be finelymachined so as to accommodate the addendum circles of the gears onlykeeping running clearance. Otherwise, interference will occur betweenthe cooperating members and this results in deformation or abrasion.Even if such exact location and fine machining are once obtained,reproduction of them at reassemb'ling cannot be expected, especiallyreproduction of complete sealing of the gear peripheries as originallyobtained will be impossible.

Accordingly it is a primary object of the invention to resolve the aboveproblems and to provide a new and improved gear pump or motor which canbe operated at a high speed and under a high pressure.

Another object of the invention is to provide a gear pump or motor inwhich means for sealing the gear peripheries is separately formed fromthe casing whereby the sealing surfaces for the gear peripheries can befinely machined and reproduced without ditficulties to accommodate thegear peripheral portions to be covered for pumping action.

Still another object is to provide a gear pump or motor in which thecasing may be shaped in a form easy to manufacture such as a cylindricalform.

A further object is to provide a gear pump or motor in which means forsealing the gear peripheries can be replaced and located exactly in therequired position within the casing.

A still further object is to provide a gear pump in which the outerlimits of the gear teeth are prevented from coming no closer to thesealing surfaces, or surfaces with which they cooperate for theproduction of pump pressure, of the pump under the action of pumppressure and upon achievement of maximum intended pump pressure than toat least a relatively light contact with said sealing surfaces.

Yet another object of the invention is to provide improved means forbalancing axial thrust of the thrust plates inserted between the endfaces of the meshing gears and each of the end walls of the casingthrough the utilization of the fluid pressure within the casing.

Still another object is to provide a pump having an improved arrangementfor filling the tooth spaces at the inlet side of the pump to enablecomplete filling of the tooth spaces at higher pump speeds than can beachieved when the fiuid is fed into the gear teeth in a direction normalto the teeth.

A still further object is to provide a gear pump having an improvedarrangement for relieving the fluid trapped in the tooth spaces as thegear teeth move into meshing engagement, and for filling the toothspaces at the inlet side of the pump as the gear teeth move out ofmeshing engagement.

A further object of the invention is to provide a gear pump or motor inwhich the unit located within the casing is automatically maintained,without compulsory positioning, in position during operation.

The gear pump or motor according to the invention comprises a casingcontaining a pair of meshing pump gears therein, gear end sealing meanson the opposite sides of the meshing gears and gear periphery sealingmeans and characterized in that said gear periphery sealing means isseparately formed from said casing and only covers the portions of thegear peripheries near the meshing area substantially along the addendumcircles of said gears.

In a preferred embodiment of the invention, the casing consists of acylindrical wall body and end closures thereof. A pair of intermeshinggears are located within said casing in such a manner that theperipheries of the gears are spaced from the inner wall of thecylindrical body of the casing. For gear end face sealing, a pair ofthrust plates are located on the opposite sides of the meshing gears.Gear periphery sealing means may comprise a member having arcuallyconcave sealing surfaces corresponding to the addendum circles of thegears. Each of the thrust plates has peripheral portions for receivingthe gear periphery sealing member so that the gear periphery sealingmember may be supported by bridging it between the two thrust plates.The peripheral portions are so shaped as to receive the sealing surfacesof the sealing member in sealing engagement. The sealing member may beurged by spring means toward the thrust plates for sealing engagementtherewith.

The cylindrical body of the casing may be secured to end closures byclamping it between the two enclosures by a plurality of at least three,and preferably four, bolts extending to the other end closure. Thecylindrical body may be fixed in a definite position by inscribing thesebelts with the inside wall of the cylindrical body.

Each of the thrust plates has at their opposite ends depressed areasspaced from the end walls of the end closures and from the end faces ofthe gears to receive the fluid pressure thereat in such a manner thateach of the thrust plates is balanced in the axial direction.

The thrust plates and gear sealing member may coact to formsubstantially axially directed inlet and outlet passages for the fluidto be introduced into the tooth spaces at the inlet side and to bedischarged from the tooth spaces at the outlet side.

Each of the two shafts for the two gears may be supported at itsopposite ends through bearings by bores recessed in the end closures ofthe casing.

Each of the thrust plates has a pair of bores which cooperate with thebores in the end closures to support two gear shafts.

The driven shaft may be supported only by the thrust plates. In thiscase, the swing movement about the drive shaft of the unit including thedriven shaft, the driven gear and the thrust plates may be prevented byinscribing the gear periphery sealing member with the inside wall of thecylindrical body of the casing.

Other objects and advantages of the present invention will be apparentfrom the following detailed descrip tion taken in conjunction with thedrawings wherein:

FIGURE 1 is a central vertical longitudinal sectional view, as indicatedby the lines 11 of FIGURES 3 and 4, of a typical form of the gear pumpembodying the present invention;

FIGURE 2 is a vertical transverse sectional view taken along the line2-2 of FIGURES 1 and 4;

FIGURE 3 is a vertical transverse sectional view taken along the line 33of FIGURES 1 and 4;

FIGURE 4 is a horizontal sectional view taken along the lines 4-4 ofFIGURES 2 and 3;

FIGURE 5 is an enlarged view of the portion indicated by the lines of5-5 of FIGURE 1;

FIGURES 6a and 6b illustrate fluid pressure distribution at the oppositeends of the thrust plate shown in FIGURE 5;

FIGURE 7 is a central vertical longitudinal secti0nal view of the gearpump showing another embodiment of the invention;

FIGURE 8 is a vertical transverse sectional view taken along the line8-8 of FIGURE 7 and FIGURE 9 is a horizontal sectional view taken alongthe line 99 of FIGURE 8.

Referring now to the drawings, first particularly to FIGURES l to 5, thepresent invention is illustrated in connection with a gear pump, but itshould be understood that the invention may be utilized in connectionwith a gear motor.

The pump includes a pair of intermeshing gears 21 and 22 mounted withina cylindrical casing 23. The casing 23 comprises a cylindrical side wallbody 24 and end closures 25 and 26 of the opposite ends of the body 24.Hereinafter one end closure 25 is referred as the front head while theother end closure 26 is referred as the end cover plate. The cylindricalbody 24 is clamped between the front head 25 and the end cover plate 26by four bolts 27 which extend through the inside of the cylindrical body24 from the cover plate 26 to the front head 25. points of a rectangleand inscribed with the inside wall 28 of the cylindrical body 24 (bestshown in FIGURES 2 and 3) so as to define and maintain the cylindricalbody 24 in position. Though not shown in the drawings, it should beunderstood that the ends of bolts 27 terminate at the front head 25 andare screw-secured thereto.

The front head 25 is recessed to contain a ball-bearing 29 and asuitable oil-seal assembly 30. A drive shaft 31 extends through the ballbearing 29 and oil-seal assembly and into the inside chamber 32 of thecasing 23 to engage and drive the drive gear 21. The gear 21 is keyed tothe shaft 31. The numeral 33 indicates the key which is fixed to thegear 21 and the numeral 34 indicates the key slot. The key slot 33 maybe longer than the length of the key 32 and have an oil passageclearance 34a at its bottom. The drive shaft 31 is supported on theopposite sides of the gear 21 by a pair of needle bearings 36 and 37which are in turn received at their outer ends within shallow bores 38and 39 recessed in the front head 25 and the end cover plate 26,respectively. The driven gear 22 is mounted on a driven shaft and keyedthereto. The driven shaft 35 is supported on the opposite sides of thegear 22 by a pair of needle bearings 40 and 4-1 which are in turnreceived at their outer ends within The four bolts are arranged at theangular shallow bores 42 and 43 recessed in the front head 25 and theend cover plate 26, respectively.

The intermeshed gears 21 and 22 are supported between a pair of thrustplates 44 and 45. The thrust plates 44 and 45 are at their inner ends insliding contact and in sealing relationship with the end faces of theintermeshing gears 21 and 22 and abut at their outer ends the end wall46 of the front head 25 and the end wall 47 of the end cover plate 26,respectively. The thrust plates have bearing bores 48, 49 and 50, 51which cooperate with the bores 38, 42 and 39, 43 to receive the needlebearings 36, 40 and 37, 41, respectively. The inner ends 48a, 49a of thebores 48, 49 are in registry with the right ends of the bearings 36, 40and the inner ends 50a, 51a of the bores 50, 51 are in registry with theleft ends of the bearings 37, 41, respectively (FIGURE 1). The innerends of the needle bearings 36 and 37 are spaced from end faces 90 ofthe gear 21. The annular space 91 between the inner end of the bearing36 and the end face 90 of the gear 21 communicates through the needlebearing 36 and an oil passage 92 to a drain port 93. The annular space91 also communicates through oil passage clearance 34a of the bottom ofthe key slot 34 to the annular space 94 between the inner end of thebearing 37 and the corresponding end face of the gear 21. The drain port93, the oil passage 92 and the oil passage clerance 34a thus formmeansfor lubricating the bearings 36 and 37. Similar lubricating means may beapplied to the bearings 40 and 41. The needle bearings 36, 37, 4t) and41 are thus maintained in position and they in turn rotatably supportthe two shafts 31 and 35 in parallel and spaced relationship.

The inside wall 28 (see FIGURE 2) of the cylindrical body 24 is spacedfrom the peripheries of the gears 21 and 22. The peripheral portions ofthe gears 21 and 22 immediately before and behind the meshing area arecovered by gear periphery sealing members 52 and 53. As it is assumedthat the drive gear 21 rotates clockwise (FIGURES 2 and 3), the sealingmember 52 covers the peripheral portions of the gears 21 and 22immediately behind the meshing area while the sealing member 53 coversthe peripheral portions of the gears 21 and 22 im mediately before themeshing area. Each of the sealing members 52 and 53 has a pair ofarcually concave surfaces 54 and 55 for covering the peripheral portionof the gear 21 and the periphery portion of the gear 22, respectively.These surfaces 54 and 55 are concentric with the gears 21 and 22 andcorrespond to their respective addendum circles with the runningclearance. The junction edge 63 of the two surfaces 54- and 55 opposesthe maximum meshing point of the gears 21 and 22. The gear peripheralsealing members 52 and 53 are elongated in directions parallel to theshafts 31 and 35 and bridge between the two thrust plates 44 and 45.Each of the thrust plates 44 and 45 has peripheral surfaces 56 and 57corresponding to the two concave surfaces 54 and 55. The sealing members52 and 53 are urged by suitable means, for example, leaf springs 58 and59, toward the gears 21 and 22 and the thrust plates 44, 45 so that theperiphery portions of the gears 21 and 22 immediately before and behindtheir meshing area may be sealed with running clearance and the concavesurfaces 54 and 55 of the sealing members 52 and 53 may be received insealing relationship by the peripheral surfaces 56 and 57 of the thrustplates 44 and 45.

The front head 25 has a fluid inlet passage 60 and a fluid outletpassage 61, best shown in FIGURE 4. The sealing member 52 is providedwith an axial flow passage 62 behind the edge 63 of the junction of thetwo arcual surfaces 54 and 55. The axial flow passage 62 communicates atits one end with the inlet passage 60 of the front head 25. The sealingmember 52 also has a pair of openings 64 and 65 on the line of thejunction edge 63 at the opposite sides of the meshing gears 21 and 22.The axial flow passage 62 communicates through these openings 64 and 65with substantially axially directed inlet passage spaces 66 and 67formed between the sealing member 52 and each of the thrust plates 44and 45. The inlet passage space 66 also communicates directly with theinlet passage 60 of the front head 25. The inlet 60, the axial flowpassage 62, the openings 64, 65 and the spaces 66 and 67 thus form inletpassage means for the fluid to be pumped.

Most of the inflow is axially introduced along the inlet passage spaces66 and 67 into the tooth spaces at the inlet side, although some of theinflow may be introduced into the tooth spaces in directions normal tothe teeth. The axially introduced inflow enables complete filling of thetooth spaces at the inlet side of the pump at higher pump speeds thancan be achieved hitherto. It is because the flow resistance is farsmaller in the axial direction than in the circumferential direction.

Outlet passage means similar to the above mentioned inlet passage meansmay be formed in the sealing member 53. The sealing member 53 isprovided with an axial flow passage 68 behind the edge 63 of junction ofthe two concave surfaces 54 and 55. The axial flow passage 68communicates at its one end with the outlet passage 61 of the front head25. The sealing member 53 also has a pair of openings 70 and 71 on theline of the junction edge 63 and on the opposite sides of the meshinggears 21 and 22. The axial flow passage 68 communicates through theseopenings 70 and 71 with substantially axially directed outlet passagespaces 72 and 73 formed between the sealing member 53 and each of thethrust plates 44 and 45. The outlet passage space 72 also communicatesdirectly with the outlet passage 61 of the front head 25. The spaces 72and 73, the openings 70 and 71, the axial flow passage 68 and the outlet61 thus form outlet passage means for the high pressure fluid. The axialflow of the discharge fluid along the spaces 72 and 73 enables the fluidtrapped in the tooth spaces to be relieved so that entrapment of thefluid in the intertooth spaces may be prevented.

In connection with the above, it is preferred that closure by thesealing member 54 of the periphery of the intermeshing gears 21 and 22at its inlet side (low pressure side) is made as close to the meshingpoint as possible. This may be obtained by extending the junction edge63 toward the meshing point of the gears 21 and 22 as close thereto aspossible. It is also preferred to reduce the size of the inlet openingsespecially, the junction opening of the inlet passage 60 and the space64, so that the tooth spaces behind the meshing point may be as small aspossible. These features are disclosed in my copending U.S. patentapplication Ser. No. 375,081 filed on June 15, 1964.

The two thrust plates 44 and 45 are of identical construction in asubstantially spectacles-shaped form, arranged symmetrically withrespect to the intermeshing gears 21 and 22. The end elevation at thefront head side of the thrust plate 44 is illustrated in FIGURE 2 andthe end elevation at the gear side of the thrust plate 45 is illustratedin FIGURE 3. As shown in FIGURE 2, the outer end of each of the thrustplates 44 and 45 has end surface areas 86 which are in contact with theend wall 46 of the front head 25 and depressed areas 87 which are spacedfrom the end wall 46 of the front head 25. The inner end of each of thethrust plates 44 and 45 has also a contact surface area 88 engaging theend surfaces 90 of the gears 21 and 22 and depressed areas 89 spacedfrom the end surfaces 90 of the gears 21 and 22, as shown in FIGURE 3.Suitable dimensioning of these non-contact surface areas 87 and 89enables the thrust plates 44 and 45 to be automatically balanced in theaxial direction whereby no axial thrust is applied to the intermeshinggears 21 and 22.

Now I consider the pressure distribution of the oppocite ends of thethrust plate 44 in a vertical and radial direction. Referring to FIGURE5, the depressed area 87 at the outer end of the thrust plate 44 has avertical and radial length a. As it is assumed that the fluid pressurein the chamber 32 within the casing 28 is P, the pressure acting on theouter end of the plate 44 is considered (P) x (a) since the fluidpressure P is applied to the whole length a. On the other hand it issupposed that the depressed area 89 and the contact area 88 at the innerend of the plate 44 have the vertical and radial lengths b and 0,respectively. The fluid pressure P acts on the whole length b of thedepressed area 89. If it may be assumed that the pressure at the space91 between the inner end of the needle bearing 36 and the end face 90 ofthe gear 21 is zero, the pressure distribution of the contact surface 83in the direction of the length c is considered as shown in FIGURE 6bsince there would be a pressure gradient due to the existence of a fluidfilm between the sliding contact surfaces 88 and 90. The total pressureapplied at the inner end of the plate 44 is, therefore, given asfollows:

Accordingly, if three factors a, b and c are selected to satisfy theformula the axial thrust forces in the opposite directions at theopposite ends of the plate 44 is completely balanced and therefore, noaxial thrust is applied to the gear 21. It will be appreciated that inorder to prevent the gear 21 from receiving thrust from the thrust plate44 the fluid pressure receiving surface area 87 at the outer end of theplate 44 must be at least smaller than the total areas of thenon-contact surface 69 and the contact surface 88 at the inner end ofthe plate 44. In the embodiment illus trated in the drawings, this isachieved by forming bores 48 and 49 at the outer end of the plate 44 forreceiving the needle bearings 36 and 40. The above mentioned means forbalancing the thrust plate 44 may be applied to the other thrust plateas well.

In order to seal around the junction opening 75 at which the inletpassage communicates with the axial fiow passage 62 and the passagespace 66, an O-ring 76 is inserted between the end wall 46 of the fronthead 25 and the contact surfaces thereto, namely'the ends of the sealingmember 52 and the thrust plate 44, so as to surround the opening as bestshown in FIGURES 2 and 4. Similarly, in order to seal around thejunction opening 79 at which the outlet passage 61 communicates with theaxial fluid passage 68 and the passage space 72, an O- ring 8%) isinserted between the inner wall 46 of the front head 25 and the contactsurfaces thereto, namely, the ends of the covering member 53 and thethrust plate 44, so as to surround the opening 79. In this mannerleakage of the pressure oil from the outlet side to the inlet sidethrough the clearance which might be produced between the end wall 46 ofthe front head 25 and the contact end surface of the member 44 isprevented. Instead of two O-rings 76 and 80, any other seal means suchas rubber packings or the like may be used. symmetrically to the abovementioned t-wo O-rings 76 and 80, there are inserted two O-rings 32 and83 between the end wall 47 of the end cover plate 26 and the contactsurfaces thereto, namely opposite end surfaces of the sealing members 52and 53 and the outer end surfaces of the thrust plate 45, so that theunit comprising the meshing gears 21 and 22, a pair of thrust plates 44and 45, and a pair of covering members 52 and 53 may be supported withinthe casing 23 in a completely balanced condition in the axial direction.It should be understood that, in addition to completely balancing theaxial thrust of each of the thrust plates 44 and 45, suitabledimensioning of the depressed areas 37 and 89 of the thrust plates 44and 45 may also be utilized for adjustment of the contact pressure ofeach 7 of the members 44 and 45 to the gears 21 and 22, which is veryimportant for both sealing and sliding engagement therebetween.

The fluid inducted from the inlet passage 60 by the pump action of thegears 21 and 22 is discharged within the casing chamber 32, theboundaries of which are defined by the cylindrical body 24, the fronthead 25 and end cover plate 26. After completely filling the chamber 32,the fluid is discharged to the outlet passage 61. During pumpingoperation, the pressure in the chamber 32 of the casing 23 is higherthan that of the inlet passage 60. This pressure difference serves tourge the covering member 52 toward the peripheries of the gears 21 and22. Accordingly, it is not necessary to apply a large biased force tothe member 52 by the spring means 58. The leaf spring 58 may be replacedby any other supporting means which merely restrict retirement of themember 52 from the engaging position. To the contrary, the pressure atthe outlet passage 61 often becomes higher than that of the chamber 32.Accordingly it would be necessary to use a leaf spring 59 having arelatively strong elasticity sufficient to overcome the pressuredifference therebetween.

In principle pumping action is sufficiently obtained with only one ofthe sealing members 52 and 53, dispensing with the other. For example,the sealing member 53 at the outlet side may be omitted from theassembly illustrated in the drawings. In this case, the outlet passagemay be formed in the cylindrical body 24.

In the embodiment illustrated in FIGURES l to 4, the shafts 31 and 35are supported through needle bearings 36, 37 and 40, 41 by the fronthead 25 and the end cover plate 26 at the bores 38, 39 and 42, 43 sothat the thrust plates 44- and 45 scarcely suffer from any radial forcefrom each shaft or torque about the drive shaft 31. If the bores 48, 49,t) and 51 for receiving the needle bearings 36, 4t), 37 and 41 arefinely machined so as to exactly center on the respective shafts 31 and35, interference which may result in abrasion will scarcely occurbetween the other parts in contact therewith.

FIGURES 7 to 9 illustrate another embodiment of the invention in which amodification is made for driven shaft supporting means. The samereference numerals as in FIGURES l to 5 indicate similar andcorresponding members or portions. Only different features and effectsfrom those described with reference to the embodiment illustrated inFIGURES l to 5 are described hereinbelow. The gear periphery sealingmembers 52 and 53 have arcual peripheral surfaces 191 and N2 which areinscribed with the inside Wall of the cylindrical body 24. No biasingmeans such as leaf springs 58 and 5? illustrated in FIGURES 2 to 4 isused with this embodiment. The bearings 40 and 41 receiving the drivenshaft 35 are not supported in fixed positions, though the outer ends ofthem are inserted in the respective shallow bores 103 and 164, since thediameter of each of the bores 103 and 194 is larger than the externaldiameter of each of the bearings 40 and 41 as shown in FIGURE 7. Thecombination of driven gear 22, the driven shaft 35 and the needlebearings 4i and 41 is supported and hung by a pair of thrust plates 4-4and 45 from the drive shaft 31. The thrust plates 44- and 45 and thesealing member 52 and 53 engaged in sealing relationship thereto aremaintained in position by engagement of either one of sealing members:52 and 53 to the inside wall 28 of the body 24 under torque about thedrive shaft 31 according to the direction of rotation of the shaft 31during operation. The limit of the swing movement of the unit comprisingthe thrust plates 44- and 45, the driven shaft 35, the driven gear 22and the sealing members 52 and 53 depends on the position of the driveshaft 31 and the shape of the peripheries 101 and 102 of the members 52and 53. In comparison with the embodiment illustrated in FIGURES l to 5,the

embodiment illustrated in FIGURES 7 to 9 is advan- L in that compulsorypositioning of the various elements may be avoided because they areautomatically maintained in position during operation. The latterembodiment may dispense with either one of the sealing members 52 and 53as well as in the former embodiment.

Although the above description has been made in connection with the gearpumps, it will be understood that any of the above embodiments may beused as a gear motor as it is without any special modification.

Particular attention is invited to the following features which greatlyimprove the pump or motor over prior structures:

(1) The sealing members 52 and 53 are formed separately from the casing23. This facilitates finely machining the sealing surfaces 54 and 55 forensuring the sealing of the gear peripheries at which pumping action iseffected. The sealing members 52 and 53 can be replaced by new ones.Reproduction of the sealing surfaces 54 and 55 is also easy.

(2) The side wall 24 of the casing 23 may be shaped in a cylindricalform. This enables manufacturing the casing more expeditiously and lessexpensively. In addition, the cylindrical form of the casing is durablein con struction and pressure distribution is uniform all over theinside wall 28 of the body. It is not necessary to finely machine theinside wall 28 of the cylindrical body 24.

(3) The cylindrical body 24 is clamped between end closures 25 and 26 bybolts 27 which extend through the inside of the cylindrical member fromone end closure 26 to the other 25. The cylindrical body is providedwith no bolt-securing holes. This may reduce the thickness of thecylindrical body 24 to a great extent.

(4) The cylindrical body 24 is maintained in position by four bolts 27which are inscribed with the inside wall 28 of the body 24. No specialmeans is required for positioning the cylindrical body 24.

(5) The'sealing members 52 and 53 bridge between the thrust plates 44and 45. This facilitates the support of sealing members 52 and 53 andboth assembling and disassembling of the unit are easy.

(6) Suitable dimensioning of the fluid pressure receiving areas at theopposide ends of the thrust plates 44 and makes it possible to balanceaxial thrust which might be applied to the intermeshing gears 21 and 22.Desirable contact pressure is also obtained between the thrust platesand the gear end faces for sealing engagement there between.

(7) Substantially axially directed inlet passage spaces 66 and 67facilitate introduction of the fluid to be pumped into the tooth spaces.Cavitation may be avoided.

(8) Substantially axially directed outlet passage spaces 72 and 73 mayprevent the entrapment of the fluid in the tooth spaces.

(9) The unit including the driven shaft 35, the driven gear 22, thethrust plates 44, 45 and the sealing members 52, 53 is allowed to swingabout the drive shaft at the non-operating state, but during operationthe swing movement of the unit is constrained by pressure engagement ofeither of the sealing members 52, 53 to the inside wall of thecylindrical body 24 of the casing 23. Compulsory rotation of the membersconstituting the unit can be avoided.

What is claimed is:

1. A gear pump or motor comprising, a casing having a side wall andopposed end closures, said casing having a fluid inlet and a fluidoutlet in one of said end closures, a pair of interrneshing gearslocated within said casing, a gear periphery sealing member covering theperipheral portions of said gears near their meshing area at the lowpressure side, said gear periphery sealing member having arcuallyconcave sealing surfaces corresponding to the addendum circles of saidgears and being floatingly supported within said casing so that duringoperation said sealing member is automatically urged by the pressurewithin said casing toward the peripheral surfaces of said meshing gears,and a pair of thrust plates located on opposite sides of saidintermeshing gears, each of said thrust plates having peripheralportions for receiving and positioning said gear periphery sealingmember therebetween, said peripheral portions being shaped as to receivethe sealing surfaces of said gear periphery sealing member in sealingrelationship, said thrust plates and a gear end sealing member coactingto form inlet and outlet passages for the fluid to be introduced intotooth spaces at the inlet side and to be discharged from tooth spaces atthe outlet side, said inlet and outlet passages being formedsubstantially in axial directions to and communicating with saidrespective fluid inlet and outlet.

2. A gear pump or motor as defined in claim 1, wherein said side wall iscylindri'cally shaped.

3. A gear pump or motor as defined in claim 1, wherein said gearperiphery sealing member is urged by spring means toward said thrustplates for sealing engagement therewith and for covering said gearperiphery portions in sealing relationship.

4. A gear pump or motor as defined .in claim 1, wherein each of saidthrust plates has at its opposite ends first recessed areas spaced fromthe end walls of said end closures and second recessed areas spaced fromthe end faces of said gears, said first and second recessed areasadapted to receive fluid pressure therein so that each of said thrustplates is balanced in the axial direction.

5. A gear pump or motor as defined in claim 4, wherein the first fluidpressure receiving surface area of each of said thrust plates is smallerthan that of the second fluid pressure receiving surface area.

6. A gear pump or motor comprising, a casing having a side wall andopposed end closures, said casing having a fluid inlet and a fluidoutlet in one of said end closures, a pair of intermeshing gears locatedwithin said casing, a pair of gear periphery sealing members coveringthe peripheral portions of said gears near their meshing area at theinlet side and at the outlet side, respectively, each of said gearperiphery sealing members having arcually concave sealing surfacescorresponding to the addendum circles of said gears and being fioatinglysupported within said casing so that during operation the sealing memberat the lower pressure side is automatically urged by the pressure withinsaid casing toward the peripheral surfaces of said meshing gears, and apair of thrust plates located on opposite sides of said intermeshinggears, each of said thrust plates having peripheral portions forreceiving and positioning said gear periphery sealing memberstherebetween, said peripheral portions being shaped as to receive thesealing surfaces of said gear periphery sealing members in sealingrelationship, said thrust plates and a gear end sealing member coactingto form inlet and outlet passages for the fluid to be introduced intotooth spaces at the inlet side and to be discharged from tooth spaces atthe outlet side, said inlet and outlet passages being formedsubstantially in axial directions to and communicating with saidrespective fluid inlet and outlet,

7. A gear pump or motor comprising, a casing having a side wall andopposed end closures, a drive gear, a driven gear meshing with saiddrive gear, a drive shaft for mounting said drive gear thereon, saiddrive shaft being supported at its opposite ends through hearings inbores recessed in said end closures, a driven shaft for mounting saiddriven gear thereon, a pair of gear periphery sealing members coveringthe peripheral portions of said gears near their meshing area at theinlet side and at the outlet side, respectively, each of said gearperiphery sealing members having arcually concave sealing surfacescorresponding to the addendum circles of said gears and being floatinglysupported within said casing so that during operation the sealing memberat the lower pressure side is automatically urged by the pressure withinsaid casing to the peripheral surfaces of said meshing gears, and a pairof thrust plates located on opposite sides of said intermeshing gears,each of said thrust plates having peripheral portions for receiving andpositioning said gear periphery sealing members therebetween, saidperipheral portions being shaped as to receive the sealing surfaces ofsaid gear periphery sealing members in sealing relationship, said thrustplates and a gear end sealing member coacting to form inlet and outletpassages for the fluid to be introduced into tooth spaces at the inletside and to be discharged from tooth spaces at the outlet side, saidinlet and outlet passages being formed substantially in axial directionsto and communicating with said respective fluid inlet and outlet, saidthrust plates supporting said driven shaft through bearings whereby theunit comprising said driven shaft, said driven gear, said thrust platesand said gear periphery sealing members is allowed to swing about saiddrive shaft at the non-operating state while during operation the swingmovement of said unit is constrained by pressure engagement of one ofsaid gear periphery sealing members against the inside wall of said sidecasing.

References (Iited by the Examiner UNITED STATES PATENTS 367,374 8/1887Deming l03l26 2,105,259 1/1938 Oshei 103-126 2,622,534 12/1952 Johnson103-126 2,742,862 4/1956 Banker 103-426 2,993,450 7/1961 Weigert 1031262,996,999 8/1961 T-rautinan 103126 3,076,413 2/1963 Hotter 103-1263,208,393 9/1965 Kosch 103-126 FOREIGN PATENTS 564,198 6/1957 Italy.

587,107 1/1959 Italy.

DONLEY I. STOCKING, Primary Examiner. WILBUR I. GOODLIN, Examiner.

1. A GEAR PUMP OR MOTOR COMPRISING, A CASING HAVING A SIDE WALL ANDOPPOSED END CLOSURES, SAID CASING HAVING A FLUID INLET AND A FLUIDOUTLET IN ONE OF SAID END CLOSURES, A PAIR OF INTERMESHING GEARS LOCATEDWITHIN SAID CASING, A GEAR PERIPHERY SEALING MEMBER COVERING THEPERIPHERAL PORTIONS OF SAID GEARS NEAR THEIR MESHING AREA AT THE LOWPRESSURE SIDE, SAID GEAR PERIPHERY SEALING MEMBER HAVING ARCUALLYCONCAVE SEALING SURFACES CORRESPONDING TO THE ADDENDUM CIRCLES OF SAIDGEARS AND BEING FLOATINGLY SUPPORTED WITHIN SAID CASING SO THAT DURINGOPERATION SAID SEALING MEMBER IS AUTOMATICALLY URGED BY THE PRESSUREWITHIN SAID CASING TOWARD THE PERIPHERAL SURFACES OF SAID MESHING GEARS,AND A PAIR OF THRUST PLATES LOCATED ON OPPOSITE SIDES OF SAIDINTERMESHING GEARS, EACH OF SAID THRUST PLATES HAVING PERIPHERALPORTIONS FOR RECEIVING AND POSITIONING SAID GEAR PERIPHERY SEALINGMEMBER THEREBETWEEN, SAID PERIPHERAL PORTIONS BEING SHAPED AS TO RECEIVETHE SEALING SURFACES OF SAID GEAR PERIPHERY SEALING MEMBER IN SEALINGRELATIONSHIP, SAID THRUST PLATES AND A GEAR END SEALING MEMBER COACTINGTO FORM INLET AND OUTLET PASSAGES